The invention relates to a surface-emitting diode emission source with an active layer used to create optical radiation whereby the created emission contains emission components spreading essentially perpendicular to a layer plane of the active layer and emission components spreading essentially parallel to this layer plane between a confinement layer consisting of semiconductor material of a conductivity type and a confinement layer consisting of semi-conductor material of a conductivity type opposed to the first conductivity type, and whereby the emission source includes a surface essentially parallel to the layer plane of the active layer from which the emission components spreading in the direction essentially perpendicular to this layer plane exit.
An example of such a surface-emitting diode emission source is a light-emitting diode (LED). LED""s with high intensity and broad modulation bandwidth are usually produced using the upside-down manufacturing technique, whereby for a typical LED structure in a InGaAsP/InP material system, a confinement layer consisting of InP of conductivity type n is applied to a substrate consisting of InP of the same conductivity type n, and the other confinement layer consists of InP of the opposite conductivity type p and includes a surface facing away from the one active layer consisting of InGaAsP and the confinement layer, as well as away from the substrate, that is in flat contact with a p-contact. A surface of the substrate facing away from the confinement layers and the active layer is in contact with an n-contact that includes an opening through which this surface is exposed, and through which the emission component spreading in the direction essentially perpendicular to the layer plane of the active layer exits from the LED.
A high level of emission output for the emission component spreading in the direction essentially perpendicular to the layer plane of the active layer and exiting from the surface of the LED may only be achieved with an undoped active layer, since doping atoms enable additional non-emitting recombination processes in the active layer.
Since on the other hand the modulation bandwidth may be considerably increased by means of a high level of doping, e.g., 2xc3x971018 cmxe2x88x923, it is not possible to achieve high bandwidths and emission outputs simultaneously only by means of suitable doping.
To solve this problem for an LED, it has been recommended to use as thin an active layer as possible, e.g., to use layers with a thickness of 0.2 xcexcm for 1.3 xcexcm-thick LED""s consisting of InGaAsP/InP within a double hetero-structure in order to increase the emitting recombination rate via high load-bearing injection without doping the layer. This method only partially solves the problem, since significantly lower emission output levels than expected result under high current conditions for the emission components spreading in the direction essentially perpendicular to the layer plane of the active level and exiting from the surface of the LED.
Another example of a surface-emitting diode emission source of the type mentioned initially is a laser diode.
For such a laser diode, a large dimension of the active layer in a direction parallel to its layer plane of about 10 xcexcm is required to achieve a high level of emission output from the emission components spreading in the direction essentially perpendicular to the layer plane of the active level and exiting from the surface of the LED. This causes the problem that the emission is also strengthened in this direction, so that the efficiency level decreases.
For a surface-emitting laser diode, arrangement of many individual lasers into an array may achieve an increased overall output of the emission components spreading in the direction essentially perpendicular to the layer plane of the active level and exiting from the surface of the laser diode.
The invention is based on the task of pointing out how the emission output for a diode emission source of the type mentioned initially may be increased from the emission components spreading in the direction essentially perpendicular to the layer plane of the active level and exiting from the surface of the diode.
In accordance with this solution, an attenuating device is provided for this diode light source that causes attenuation of the emission components spreading in the direction essentially parallel to the layer plane of the active level.
In an advantageous embodiment example of the source based on the invention, the attenuating device includes a layer formed of emission-absorbing material within a confinement layer extending parallel to the layer plane of the active layer.
A layer of emission-absorbing material may be present on both sides of the active layer. A layer of emission-absorbing material should be arranged sufficiently close to the active layer.
The attenuating device may alternatively or additionally include adjacent emission deflection points and/or emission diffusion points in the direction parallel to the layer plane of the active layer to divert an emission portion of the emission components spreading in this parallel direction from this direction to a direction essentially perpendicular to the layer plane of the active layer.
Emission deflection points and/or emission diffusion points may be arranged in or near the active layer. By means of them, the emission components spreading in the direction parallel to the layer plane of the active layer may be diffused and attenuated. Thus, the occurrence of unfavorably strong Amplified Spontaneous Emission (ASE) may be prevented without influencing the surface emission.
An advantageous simultaneous optimization of both light output and bandwidth is produced by a source based on the invention. Moreover, the problems described above in connection with an LED or laser diode are advantageously solved whether the source based on the invention is in the form of an LED or a laser diode.
If a source based on the invention is in the form of an LED, a thin active layer may be advantageously used in order to achieve a large bandwidth, since the ASE is attenuated in the direction parallel to the layer plane of the active layer by the attenuating device.